[FFmpeg-devel] [PATCH] avcodec: add minimal teletext subtitle decoder

Marton Balint cus at passwd.hu
Thu Apr 26 22:12:15 EEST 2018

On Thu, 26 Apr 2018, Aman Gupta wrote:

> On Thu, Apr 26, 2018 at 8:12 AM, Nicolas George <george at nsup.org> wrote:
>> Aman Gupta (2018-04-26):
>> > Another reason I discounted libzvbi is because it seems unmaintained,
>> > without a new release is over 5 years.
>> Did the teletext standard evolve in the past five years?
> I don't know, but there it is atleast one bug causing tests to fail on
> macOS which has been unfixed for 4 years.
> I managed to install libzvbi by hand and try it out. With `-txt_format
> text`, the generated output text is the same but without positions/colors.
> The ASS positioning code could be ported over, but it looks like
> vbi_print_page_region() strips out all the color information so there
> doesn't seem to be an obvious way to support text coloring.
> The zvbi decoder also hardcodes a (configurable) 30s end time per subtitle,
> which causes them to pile up on the screen and not disappear when they're
> supposed to. The logic from my decoder could also probably be ported over,
> under a new `-real_time 1` flag like I added to ccaption_dec last year.
> Here's a side by side comparison:
> https://dzwonsemrish7.cloudfront.net/items/2x1z3k0C0X3v0Z2j1F3b/teletext-sub-comparison.jpg
> I agree it would be ideal to have only one teletext decoder that works for
> everyone. However I'm done with my teletext project, and don't have time
> right now to redo all that work in the zvbi encoder. I also live in an ATSC
> region and don't use teletext myself, so I don't really care whether or not
> my decoder is merged into ffmpeg. I only shared it because some people on
> IRC expressed interest.

I will try integrating the ASS formatting part of your patch to the 
libzvbi decoder, and see how it goes.


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